It is known to provide spring motors having longitudinally symmetrical tapered flat tapes that produce variable reactive forces. Early examples are disclosed in a 1952 U.S. Pat. No. 2,609,193 to Foster, and in later U.S. Pat. Nos. 3,194,343 and 3,194,344 to Sindlinger. Foster discloses a so-called “A”-type spring motor, and Sindlinger discloses a so-called “B”-type spring motor.
In a B-type motor, a length of pre-stressed tape, or ribbon, is wrapped around first and second spools rotatable about spaced parallel axes. Each spool has a circular hub and a pair of circular flanges extending outwardly from the hub in spaced parallel relation. The tape is wrapped about the spool hubs such as in the manner described in referenced Sindlinger patents to form a spring motor assembly. In such an assembly, when one of the spools, such as the driver spool, is rotated about its axis, the tape element reacts as it separates from the driven spool, and causes either more, or less, torque to be required to rotate the driver spool. Either spool may be connected to a variety of prime mover mechanisms, such as a lanyard wrapped about a pulley, so that linear motion of the lanyard is converted to rotational motion. A simple practical application of this mechanism can be found in counterweighting window sashes and window treatments wherein the present invention also finds utility.
In published, but abandoned, U.S. Patent Application published as No. 2009/0108511 A1, several variations of a tapered spring tape are disclosed. In one such variation, illustrated in FIGS. 10 and 11, the tape has a single longitudinal straight edge and a single tapered edge extending between opposite ends. While such a tape may provide some theoretical advantages, the Published Application does not disclose any information about how to manufacture such a tape efficiently.
While the disclosed patented and published flat tapered tape spring motor mechanisms may function satisfactorily for their intended purposes, none is capable of being manufactured efficiently. Thus, there is a need for a flat tapered tape spring that is capable of being manufactured efficiently using commercially available equipment employed in a novel process. Moreover, there is a need for a tapered flat tape B-motor that can be used effectively in product display tethering applications, such as currently provided by the PULLBOX® product manufactured by applicant's assignee Vulcan Spring and Manufacturing, Inc. of Telford, Pa.